1. Field of the Invention
The present invention relates to a metallurgical furnace unit but includes a cylindrical furnace body which is adapted for rotational and/or pivotal or similar movements, these movements being made possible by means of at least one ring mounted outside the furnace body. The invention relates more specifically to a top-blown rotary converter.
2. Description of the Related Art
By "metallurgical furnace unit" is generally meant process apparatus with which pyrometallurgical unit processes are carried out at the highest temperatures required for the unit process concerned. The term "metallurgical furnace unit" as used in this document also includes furnace units in which metallurgical processes other than strictly pyrometallurgical processes are carried out, for instance inorganic high temperature processes. The furnace units may be smelting furnaces, kilns, or heat-treatment furnaces of different kinds, both for batch-wise processes and continuous processes. Such furnace units may be provided with one or more rings around the furnace body, these rings being generally known as mounting rings which can have the function of slide rings, tilt rings or support rings. A common feature of these rings is that they are seated outside the actual furnace body, i.e. outside the circular outer casing wall of the unit.
Many different types of metallurgical furnace units are available, each being designed for the specific movements to be carried out by said units. For instance, there are known to the art various kinds of continuously operating rotary furnaces which include several rings that rest on rollers, which may be drive rollers or solely support rollers, with the furnace slightly inclined. It is also necessary to design horizontally operating converters for different types of movement, e.g. a tilting movement or rotational movement about their respective long axes. Such converters also rest on rollers, either freely rotating or driven rollers, and can be tilted or rotated with the aid of said rollers. Also known in this art is a group of furnace units that can be commonly designated non-horizontal converters. A common feature of such converters is that they can be tipped or rotated about an axis that extends transversely to their longitudinal axes, and that they have a bottom part and an upper part which includes an opening opposite said bottom part in the longitudinal direction of the converter. Such converters may be upright converters of the type known as LD, Thomas, OBM or BOLD converters, or inclined rotary converters, often called TBRC or Kaldo converters.
In addition to being able to tilt and/or twist, rotary converters shall also be capable of rotating about their longitudinal axes, often at a relatively high speed. The converters are rotated in conjunction with mixing operations and reaction processes for instance, and are swivelled in conjunction with charging, blowing, slag withdrawal, furnace tapping and furnace relining operations.
A common problem with all metallurgical furnace units of the aforedescribed kind is that of mounting the ring or rings around the furnace body without causing complications in use as a result of the large temperature variations that occur in the furnace unit and the furnace walls during operation. These temperature variations propagate in both the space dimension and the time dimension. Moreover, the heavy weight of such furnace units and their contents cause problems when the furnace units shall be manoeuvred, i.e. rotated and pivoted or swivelled during the metallurgical processes. As a result of these temperature variations, the furnace unit will expand and contract alternately, both radially and longitudinally. Moreover, expansion of the furnace unit is not uniform over the whole of furnace body. Consequently, problems occur when the rings are mounted directly on the outer furnace wall, since the rings do not follow the movements of the furnace wall caused by thermal expansion. Consequently, the rings are either mounted with a predetermined amount of play or clearance or so that the rings are able to slide around the furnace body. However, this, in turn, results in undesirable gaps between rings and furnace body, which results in heavy wear on both rings and furnace walls, particularly because of the heavy loads that must be brought into motion when using the furnace.
Various constructive solutions to these problems have been proposed in recent years, such as the securement of rings and furnace body with various types of movable bolt connections, for instance. One such construction is described in GB-A 1218441, according to which a mounting ring is fastened to the furnace wall of, e.g., a Kaldo converter with the aid of supports and "resiliently" extensible bolts disposed in apertures of elongated cross-section which extend through the ring and the support parallel with the longitudinal axis of the furnace, such that the longitudinal axis of each opening that extends radially of the furnace at opposite ends of the bolts are respectively supported by bearing surfaces provided on the ring and support. This enables each bolt to pivot in the radial plane. The bolts thus actually function as some kind of obliquely outwardly acting link.
A common drawback with all known and tested constructions in which the rings are mounted on the furnace body is found in the enormous amount of wear on the furnace bodies, which demands frequent and regular maintenance work and therewith heavy maintenance costs are of cause entailed. It is for this reason that these known and tested constructions have not met with any real success. Naturally, the larger the furnace unit constructed, the greater the problems caused, since wear on the furnace bodies increases at higher loads. In view of the fact that charge weights often reach 100 tonnes, the aforesaid problems are highly significant. Any undesirable play in the furnace construction can become highly troublesome and result in prohibitive wear problems and, at high rotational speeds, also in a rotational imbalance which further worsens the wear problems.
DK-A 68786 proposes a solution in which support rings are connected to the outer surface of the furnace by means of so-called elastic supporting elements. These supporting elements are rigidly fastened in both the outer cylindrical surface of the furnace and the support rings, for instance with the aid of several rows of bolts. Each supporting element is forced to bend in order to take up furnace-body movements caused by thermal expansion. Because the intrinsic elasticity of the material is utilized in this respect, the solution can be effected technically and is also apparently a neat solution in the present context. To facilitate utilization of the elastic properties of such supporting elements, it is suggested that said elements are given the form of plates, iron shapes or profiles, or like elements, and that they are also connectable to a short cylindrical member at the end where said supporting members are joined to the furnace casing. When the furnace unit includes a casing, the casing will preferably include axial slots that facilitate bending of the elastic supporting members. In connection with the advent of the present invention, calculations were made on the earlier proposed, but never tested (as far as we are aware) attempts to solve the aforesaid problems associated with the thermal expansion of furnace bodies that include supporting rings. However, mechanical strength calculations made with modern computerised FEM analysis showed that the fatigue stresses occurring with heavy loads and a large number of load alternations (furnace rotations) in such a construction were so high as to subject the furnace body to the danger of fatigue fracture at several locations. This was particularly due to stress concentrations in the slot radii and attachment holes, which greatly reduced the useful life span of the construction. One reason why the apparently defective known construction has not been put to general use is perhaps because of negative experiences obtained in any test runs carried out. If so, it is today possible to explain such negative experiences with the aid of modern computerised strength calculations.
Although the invention is not restricted to rotary converters, as mentioned in the introduction, it is particularly with such furnace units that the problems relating to the securement of mounting rings is greatest, partly because of the special operating conditions prevailing with such converters, where it is necessary to both rotate and tilt, or pivot, the converter. These problems are well known to all metallurgists who have experience with rotary converters.